1. Field
An aspect of the invention is related to communication apparatuses including a transmitting apparatus and a receiving apparatus, a transmitting method, and a receiving method for transmitting/receiving wireless signals.
2. Description of the Related Art
In wireless communication systems including a mobile communication system, wireless signals are transmitted to a receiving apparatus from a transmitting apparatus. Packet data or the like is an example of the wireless signals. There are various data which is stored in a data part of the packet data. The data is not limited to text data and image data, but may include audio data or the like. If the wireless signals are not transmitted continuously, the transmission of the wireless signal is generally performed at a predetermined interval. For example, the transmission is performed every 20 ms.
However, there is no guarantee that the receiving apparatus can successfully receive the wireless signal even though the transmitting apparatus transmits the wireless signal. That is, a transmit signal is influenced by a propagation channel (path) (e.g., a fading channel) because the transmission and reception are performed wirelessly. Accordingly, a receive signal that the receiving apparatus obtains by receiving the transmit signal may not be correct. The transmit signal can be error-correcting coded, and it is possible to generate an appropriate receive signal by error-correct encoding in the receiving apparatus. However, the error may not be corrected completely depending on the extent of the error, so that the receiving apparatus may not obtain the appropriate receive signal.
In consideration of the above descried matter, there is a technology for performing a retransmission from the transmitting apparatus by determining reception result of the transmit signal in the receiving apparatus and feeding back the reception result to the transmitting apparatus.
FIG. 1 shows a known method of data transmitting/receiving processing in which the retransmission control is introduced.
As described in FIG. 1, the transmitting apparatus transmits the data (e.g., audio packet data) in turns every 20 ms. The receiving apparatus attempts to receive the transmitted data. Then the receiving apparatus transmits an ACK signal when the data is successfully received. The transmitting apparatus recognizes that the transmission was performed successfully if the ACK signal is received and then transmits other transmit signal (e.g., a next transmit signal which is to be transmitted to the same receiving apparatus) at next transmit timing. However, as described in FIG. 1, when the receiving apparatus could not receive the data successfully since a third transmission became an error because of the influence of the wireless channel, the receiving apparatus transmits a NACK signal. The transmitting apparatus recognizes that the transmission was not performed successfully if the NACK signal is received and then performs the retransmission. Thus, the receiving apparatus further receives the retransmitted data. When the reception of the retransmission is successful, an ACK signal is transmitted from the receiving apparatus and then next data is transmitted from the transmitting apparatus at the next transmit timing. Accordingly, even if a first transmission fails, it is possible that one or more than one retransmission makes the transmission a success by introducing the retransmission control.
As for the above described retransmission control are described in 3GPP TS25.212, 3GPP TS25.321 and 3GPP TS36.212.
As described previously, introducing the retransmission control increases chances of successful data transmission from the transmitting apparatus to the receiving apparatus. However, it is difficult to perform a control such as to perform an intermittent reception simply at a predetermined interval, because the retransmission control is performed (inserted).